Houston’s wacky iPhone temperature mystery — solved!

As you may recall, earlier this summer the iPhone’s weather app was showing consistently hotter than normal temperatures for Houston. Like 5 to 6 degrees hotter than what temperatures actually were across much of the city.

I’ve written about this a couple of times, and while the problem was fixed a few weeks ago, some mystery remained about how it has been fixed. To that end I’m happy to report, after I griped about public relations at The Weather Channel, they’ve done a commendable job in answering my questions.

So here, in detail, is what happened.

First, to be clear, I’m talking about the standard weather app that’s on the homepage of the Apple iPhone. It looks something like this:

I'm a champion circle drawer.

And if you tap that app, and search for “Houston,” it pulls up the following page that looks something like this.

Sorry, no fancy graphic artistry on this one.

The top reading — 82 degrees — represents the “current conditions” in Houston. The next six readings represent “forecast conditions” for the city.

For the longest time, for “current conditions” the iPhone was pulling meteorological data from a site known as KMCJ (also known as USTX0617), the helipad at Memorial-Hermann Hospital in the Texas Medical Center, some 200 feet above the ground.

This is really problematic. For example, at 3 p.m. Tuesday, Houston Hobby Airportwas reporting 94 degrees. At the same time, KMCJ was reporting 100 degrees.

Owned by the Texas Medical Center, it’s a valid meteorological site as it meets FAA Aviation weather requirements. A few years ago, when Yahoo! got the contract from Apple to provide data, it turned to The Weather Channel for weather information.

The Weather Channel chose the KMCJ site because it was the closest “validated” site to the precise latitude and longitude of Houston 29.7631° N, 95.3631° W. Interestingly this latitude and longitude is exactly one block north of where I park my car every day.

What they didn’t realize, until I began reporting on this issue, is that while the site was great for aviation weather, it stunk for providing real-world conditions at the surface. To their credit, they changed it after I called attention to the matter. The Weather Channel is also having a related issue in Baltimore, as it turns out.

So what’s the iPhone reporting now? It’s complicated because there are two datasets, explained Ian Miller, senior vice president of weather systems at The Weather Channel.

For the “current conditions” number, that’s now coming from Houston Hobby Airport. In the United States, when you search for a location in the weather app, it defaults to the closest of 1,500 National Weather Service reporting stations. Previously in Houston that was the Helipad site, but it’s now been removed from the database. So now it’s Hobby, which is a pretty good default location.

For the “forecast conditions,” ironically, when you enter “Houston” in the iPhone weather app, it still defaults to conditions on the ground in the Texas Medical Center. This is because “forecast conditions” uses a different database, which has forecasts for 10,000 locations around the country, including climate co-op stations. I’m assured the forecast is for conditions “on the ground,” not 200 feet up.

So that’s what you get as a default for “Houston.” What about other kinds of searches (i.e., you can search zip codes) in the Apple weather app?

When you enter something besides “Houston” in the app’s search box — say a zip code — it’s possible to get hourly conditions for one site close to that location, and “forecast conditions” for a site even closer to that location. That’s because there are more locations for “forecast conditions” and you’re likely to end up with a more nearby site.

I’ll let The Weather Channel have the last word.

“Weather.com and our apps have pretty good user feedback, and we track that very actively and monitor it,” Clayton said.

In other words, if users find more issues with weather.com’s data like that with the helipad data in Houston, they want to hear about it.